By Thom. H. Dunning Jr., Raymond A. Bair (auth.), Clifford E. Dykstra (eds.)

That there were notable advances within the box of molecular digital constitution over the last decade is apparent not just to these operating within the box but additionally to a person else who has used quantum chemical effects to steer their very own investiga tions. The growth in calculating the digital constructions of molecules has happened in the course of the actually inventive theoretical and methodological advancements that experience made computationally tractable the underlying physics of electron distributions round a set of nuclei. even as there was examine capable enjoy the nice advances in desktop know-how. The starting to be sophistication, declining bills and lengthening accessibi lity of pcs have allow theorists follow their the right way to prob lems in nearly all components of molecular technology. for this reason, every year witnesses calculations on better molecules than within the yr ahead of and calculations with larger accuracy and extra com plete details on molecular homes. we will without doubt count on persevered methodological strengthen ments of actual end result, and we will be able to additionally see that the improvement in computational strength isn't approximately to decelerate. the new creation of array processors, a number of processors and vector machines has yielded an important acceleration of many varieties of computation, together with operations usually played in quantum chemical stories. using such new computing energy to the ut so much has required a few new rules and a few reformulations of current methods.

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One easily gets a performance ~ 100 MFLOPS, roughly a factor of 5 better than for the CYBER 205. The state of affairs is much better for the integral transformation, where the transformation itself can in fact be done at ;:: 50 ;-1FLOPS on a single pipe CYBER 205. In the following table we compare timings of the program as it stands now with those given by Werner and Reinsch in this volume and those of Saunders and van Lenthe (14). 58194 155. 8. 0 33. 37166 present 144. 8 13. 1 49. 32737 107. 7.

NOW, the wavefunction of any physical two-electron state has to be independent of the orbital set chosen: 24 W. MEYER ET AL. ~cd (6 ) '¥Cd C Substitution using eq. (5) yields the relation between C and C· ~cd C (8) a The wave function has the form of a trace over a tensor product of the CSFs with a tensor of coefficients which transforms contragradient to the CSFs. It is important to note here that this particular transformation of the coefficient matrix is incompatible with the notion of a nonredundant orthonormal set of spin adapted CSFs.

The order in eq. (1) above does not reach acceptable levels even for the CRAY unless high quantum numbers are involved and this leads us to the third approach to program design. This last option relies on our knowledge that normal calculations involve many more than one block of integrals and those of the' same quantum numbers require (almost) exactly the same treatment. A parallel approach is a natural suggestion and that vector processor hardware is serial pipelined rather than parallel is irrelevant.